Electronic timer control for inflatable boots on aircraft



June 29, 1948. w B. POND ET Al. 2,444,209

ELECTRONIC TIMER CONTROL FOR INFLATABLE BOOTS ON AIRCRAFT Filed Deo. 18, 1944 2 Sheets-Sheet 1 I N VEN TORS June 29, 1948. w. B. POND ET AL 2,444,209

. ELECTRONIC TIMER CONTROL FOR INFLATABLE BOOTS ON AIRCRAFT Filed Dec. 18. 1944 2 sheets-sheet 2 IN VEN TORS Frank ,I Hari' willialw B. Rand claims.

Patented- June 29, 1948 UNITED STATES PATENT OFFICE ELECTRONIC'IIMER CONTROL FOR IN- FLATABLE BOOTS N AIRCRAFT William B. Pond, Burbank, Calif., and Frank J. Hart, Englewood, N. J., assignors to Bendix 'Aviation Corporation, Teterboro, N. J., a corporation of Delaware Application December 18, 1944, Serial No. 568,790

13 Claims.

` l The present invention relates to a control systemy and more particularly to an electronic timer for controllingthe inflation of suitable inflatable `.units or boots mounted upon airplane wings and other airfoils and surfaces of aircraft for the pur- -pose of preventingfthe accumulation of ice.

The basic idea of the inflatable rubber is to permit ice to form on a surface and then to distort l that rsurface so as to break the ice into pieces free from the surface which can be carried away by the airstreams, as shown `for example in the Patent No. 1,990,8i to David Gregg, dated Feb-'- ruary l2, i935. The present invention relates to improvements in a timer system such as shown `inthe copending application of Donald M. Lawrence, David Gregg and Myron L. Taylor, Serial The latter system has provided means for infiating and den viiating the boot-s, including means whereby the control of such boots is reduced to an electrical circuit embodying suitable solenoids for loperating the boots.

An object of the present invention is to provide an improved variable cycle timer forsuch system.

' Another object is the provision of novel means .for terrmnating the operation of the timer in a home position.

Another object is to provide novelmeans whereby single cycle operation of the system may be effected so that each boot may Ibe inflated and rdeiiated in correct sequence and then held in a deflated condition until such time as the cycle l of operation is repeated.

Another object of the invention is to provide novel. means for effec-ting automatic operation of :an ice eliminating system, including adjustable means for varying 'the time interval between cycles of operation.

Another object of the invention isk to provide novel means for effecting manual control of the boots vwhereby any one of aseries of boots mai7 be .selectively inflated for as long a time inter- `val. as desired and as often as desired.

Another object of the invention is to provide novel means for providing automatic operation vof the system and manual control of the boots during such automatic operation.

Other objects` and advantages of this invention are yset forth in the following description, taken `with the Yacconipanying drawings; and the novel features thereofare pointed out in the appended Thev disclosure, rhowever, is illustrative only and WemaymaKe changes in detail, espe- 4cially yin'matters of shape, size, and arrangement of parts within the principle of the invention, to

the full extent indicated by the broad and general meanings of the terms in `which the aD- pended claims are expressed.

In the accompanying drawings which form a part ofA this specification like reference characters indicate like parts in the several views where- VFigure l illustrates diagrammatically one form of the electronic de-icer control.

Figure 2 illustrates diagrammaticallythe control system as applied to an aircraft -de-icer system.,

Figure 3 is a cross-sectional view taken along the line 3-3 of Figure 2 and looking in the direction of the arrows.

In iii-grue 4 `our control system is illustratedfas applied to an aircraft ice eliminating `system such as described in the copending application of Donald M. Lawrence, David Gregg, and Myron L. Tayloig-Serial No. 4298248, iiled August 11, 1943, and iny thecopending application of Myron L. Taylor and Samuel K. Lehman, Serial No. 498,249, filed August l1, 1943, now U. S. Patent No. 2,405,- 362, granted August 6, 1946, and assigned to Bendix Aviation Corporation.

1n the disclosure of Figure 2 to which oui` novel control system maybe applied there is shown an airplane comprising a fuselage I having Wings 2 and rear vertical and horizontal stabilizers 3 and 4 respectively.

A plurality of expandable boot unitsfof the type vdisclosed in the aforenoted Patent No. 1,990,866 to David Gregg are mounted at the leading edge of the forward wing 2. rlhese expandable Vunits are indicated on the forward port wing by the numerals 5, t, 'I and t, while on the starboard wing corresponding expandable units are indicated by numerals, 5A, 5A, TA, and 8A. Expandable units are further provided atthe leading edge of the rear horizontal stabiliaers indicated at the port side by the numeral 9 and at the Astarboard side by the numeral 9A. Afurther eX- pandable unit I!) is provided at the leading edge of the vertical stabilizer 3 asshown in Figure 2.

Each of said expandable units are constructed of elastic rubber-like material suitably reinforced and secured upon the Wing or other airfoil and each unit comprises one or more inflatable tubes. For simplicity of illustration each boot is shown as comprising three inflatable tubes, indicated in Figure 3 by the numerals I I, l2 and I3. The tubes Il and I3 are arranged for inflation and deilation together, While the tube I2 is separately inflatable from the tubes I I and I3.

"-'Extending'spanwise yof the forward yWings 2 are main air pressure and suctionconduits indicated by numerals I4 and I5, respectively. The air pressure conduit |4 is connected by conduits I5, I'I, I8 and I9 to suitable air pressure pumps 20, 2|, 22 and 23 driven by the airplane cmotors 24, 25, 26 and 21, respectively. The suction conduit I is connected by a conduit 28 to a suction conduit .29 leading from the pump 22.

As shown in Figure 2, separate distributor valve units 39 are provided for independently controlling the expansion and contraction of the aforesaid units. The said distributor valves 30 are connected directly into the main pressure and suction lines I4 and I5, respectively, as shown in Figure 2, and control the inflation and deiiation of the in4 latable tubes I I and I2 of the unit, shown in Figure 3, through a conduit 3| while the tube I2 is controlled through a conduit 32. The exhaust pressure from said tubes II, I2 and I3 is conducted outward through the exhaust or overboard conduit 33 during deation of the tubes Il, I2, and I3.

Provided at the opposite ends 0f the spanwise extending conduits I4 and I5 are manifold unloading valves 34 and 35 for releasing the pressure Within the line I4 when the boots are not in use. The manifold unloading valves are preferably of the type described in the copending application of Myron L. Taylor and Samuel K. Len-- man, Serial No. 498,249, led August ll, 1943, now U. S. Patent No. 2,405,362, granted August 6, 1946, and assigned to Bendix Aviation Corporation. The valves 34 and 35 are controlled by solenoids X and Y electrically operated through .suitable electrical connections as shown` in Figure 1, whereby upon energization of the solenoids X and Y the release valves 34 and 35 are closed, while upon cle-energization of the solenoids X and Y the pressure within the manifold I4 is unloaded to atmosphere through the valves 34 and 35.

A suitable relief valve 36 is mounted intermediate the opposite ends of the spanwise extending pressure conduit I4 for relieving the pressure Iwithin the conduit I4 upon the salme increasing beyond a predetermined maximum value.

There is connected at the relief valve 36 a second pressure line 3l which extends longitudinally of the plane to a distributor valve 38 positioned at the rear of the plane. The distributor valve 38 is arranged for controlling through conduits 39 and 40 the inilation and deflation of tubes provided within the expandable units 9, 9A and I0 which correspond to the tubes I2 yand I3 previously described. The exhaust pressure from. the tubes during deflation is conveyed outward through conduit 4|.

A suction line 42 connects the said distributor valve 38 to the Kmain suction line I5. A second suction line 43 extends from the distributor valve 38 to the low pressure area of the plane. A suit- -able control valve 44 regulates the line 43 so as to lopen the same upon a decrease in the suction force exerted at the line 42 below a predetermined minimum value so as to exert in such event an added suction force to the line 42.

The distributor valves 30 and 38 are controlled by a pair of solenoids mounted in each as explained in the aforenoted copending application of Don-ald M. Lawrence, David Gregg, and Myron. L. Taylor, Serial No. 498,248, filed August 11,. 1943. rI'he distributor system shown in Figure 2 is symmetrical, in that the units mounted on the starboard side of the airplane follow the arrangement on the port side.

Moreover, as shown in Figure 1, the solenoids:

4 A, B, C, D, E, F, G, and H are provided in pairs. The solenoids of each pair are mounted at opposite sides of the airplane for operating correspondingly positioned units, as shown in Figure 2, and further the solenoids of each pair are arranged for joint energization, as shown diagrammatically in Figure 1. The solenoids J and K control the distributor valve 38. The solenoids A, B, C, D, E, F, G, H, J, and K are controlled by the electronic timer control, as will be explained.

As described in detail in the aforenoted application of Donald M. Lawrence, David Gregg, and Myron L. Taylor, Serial No. 493,248, filed August 11, 1943, the said solenoids are arranged so that upon energization thereof the boot tube or tubes controlled thereby will be inflated, while upon de-energization thereof the said boot tube or tubes will be deflated. As shown in Figure 2 a cable 45 carries the necessary electrical conductors for controlling the energization of the respective solenoids. The time interval of operation for each unit, and the time interval between cycles of operation, will oi course be determined by the electronic timer of Figure 1.

Now referring to the drawing oi' Figure l there is provided a suitable source of electrical energy indicated by the numeral |00 which may be connected `into the novel control circuit by operation of a double pole switch |0| having the interconnected arms |02 and |03. The positive terminal of the source of electrical energy |00 is connected by an electrical conductor |04 to the switch arms |02 and |03 respectively,

The negative terminal of the source of electrical energy |00 is connected by a conductor |05 to one terminal of each of the respective control solenoids A, B, C, D, E, F, G, H, J, K, X and Y. The conductor |05 is also connected to one terminal |06 of a motor M.

As will be readily seen, with the switch |0| in the position shown in Figure 1, the circuit to the respective control solenoids and motor M is open and the de-icer system is not in operation.

The system may be placed in operation by manually shifting the switch II so as to actuate the switch arm |02 and |03 in a clockwise direction closing switch contacts IIO and III. The switch contact I0 is connected by an electrical conductor I2 to the opposite terminal of the solenoids X and Y from that to which the electrical conductor |05 is connected and thus the solenoids X and Y are energized so as to close the pressure release valves 34 and 35 as previously explained. The circuit for energizing the solenoids X and Y is connected from the positive terminal of the source of electrical energy |00 through conductor |04, switch arm |02, contact I0, conductor I2, through electromagnets X and Y, and conductor |05 to the negative terminal of the source of electrical energy |00.

The switch contact I is connected through an electr-ical conductor I|3 to another terminal |I4 of the motor M. Thus upon switch arm |03 closing the contact I|| the motor M is energized by the source of electrical energy |00.

A switch |20 is provided in the circuit ||3 for connecting a resistance |2I in or out of the circuit I I3 for controlling the speed of the motor M. Thus with the switch arm |20 in the position shown in Figure 1 closing a contact |22 leading to the resistance |2I, the resistance |2| will be cut into the circuit of the motor M and the motor M will be driven at a relatively slow speed.

However, upon the switch arm |20 being manually adjusted so as to close switch contact |23 the There will thus be eiected a discharging circuit; for the condenser 54 whichmay be traced from the positive terminal of the source of electrical energy through conductor |04, switch armA |02, contact |50, conductor |19, resistance |18, switch arm |16, contact |15, resistance |14, resistance |12, contact |1|, conductor |10, conductor |51, condenser |54, conductor |52, switch contact |55, switch arm |60, conductor IBI, and conductor to the negative terminal of the source of electrical energy |00.

Thus electronic energy from the negatively charged plate |56 of the condenser |54 will flow to the positive terminal of the source of energy |00, the time interval for discharging the condenser |54 being determined by the resistance values cut into the line ||19 by the switch arm |16. Thus by varying the value of such resistance the discharge time interval may be controlled.

Connected to the conductor |51 is a conductor |80 leading to a resistance |8| which has the opposite end thereof connected to the control grid |48 through a conductor |82. Thus during the discharge of the condenser |56 a negative charge will be placed on the control grid |48, while a positive charge will be placed on the cathode |46 through the conductor |52, so as to restrain the firing action of the electronic valve |44.

An electrical conduit |90 leads from the plate |49 of the electronic valve |44 to a solenoid |9|. A second conduit |92 leads from the solenoid |9| to a contact |93 normally closed by a relay switch arm |94, biased under spring tension to the closed position. A conductor |95 leads from the relay switch arm |94 to the conductor H2, which in turn leads through switch arm |02 to the positive terminal of the source of electrical energy 00.

Thus upon the condenser |54 becoming discharged sufliciently to permit the firing of the electronic valve |44, the solenoid |9| will become energized. The energizing circuit for the solenoid |9| is connected from the positive terminal of the source of electrical energy |00 through conductor |04, switch arm |02, contact |50, conductor H2, switch |94, contact |93, conductor |92, solen noid |9I, conductor |90, plate |49, cathode |46, conductor |52, contact |55, switch |60, conductor ISI, and conductor |05 to the negative terminal of the source of electrical energy |00.

The solenoid |9| controls a relay switch arm I 96 normally biased under spring tension to an open position relative to a relay contact |96A. The arm |96 is electrically connected to conductor |19 leading to the positive terminal of the source of electrical energy |00 through switch arm |02.

The relay contact |96A is connected by an electrical conductor |91 to a solenoid |98. The opposite terminal of the solenoid |98 is connected by a conductor |99 to a conductor 200 which leads through a resistance 20| to the conductor |05 leading to the negative terminal of the source of electrical energy |00.

Thus upon energization of the eelctromagnet I9| as upon the firing of the electronic valve |44 the switch arm |96 will be actuated by the electromagnet force of the solenoid |9| so as to close contact |90A causing energization of solenoid |98. The energizing circuit for the solenoid |98 is connected from the positive terminal of the source of electrical energy |00 through conductor |04, switch arm |02, contact |50, conductor |19, switch arm |96, contact |96A, conductor |91, solenoid |98, conductor |99, conductor 200, resistor 20|,

and conductor |05 to the negative terminal of the source of electrical energy |00.

Energization of solenoid |98 will in turn cause a relay switch arm 203 to close contact 204 and actuate spring biased switch arm |94 so as to open contact |93, previously described, whereupon the solenoid |9| will be deenergized.

Switch arm 203 is connected to electrical conductor |91, while switch contact 204 is connected through switch arm |94 to a conductor 2 I0 leading to the relay switch arm |43 for a purpose which will be hereinafter explained.

It will be seen that upon switch arm 203 closing switch Contact 204, a holding circuit will be closed through conductors |95 and |91 so as to maintain the electromagnet |98 energized, upon solenoid |9| being deenergized causing relay switch arm |96 to open contact |96A, as previously described. The holding circuit for the solenoid |99 is connected from the positive terminal of the source of electrical energy |00 through conductor |04, switch arm |02, contact |50, conductor I2, conductor I 95, switch arm 94, contact 204, switch arm 203, conductor |91, solenoid |98, conductor |99, conductor 200, resistor 20|, and conductor |05, to the negative terminal of the source of electrical energy |00.

Leading from the conductor |91 is a conductor 2|5 which connects the conductor |91 to the conductor ||3 leading to the motor M previously described. It will be thus seen that upon relay switch arm |96 closing contact |96A the motor M will be energized and the relay switch arm 203 will upon the closing of contact 204 effect a holding circuit for maintaining the motor M energized after the opening of contact |96A. The holding circuit for the motor M is connected from the positive terminal of the source of electrical energy |00 through conductor |04, switch arm |02, contact |50, conductor H2, conductor |95` switch arm |94, contact 204, switch arm 203, conductor I9?, conductor 2|5, conductor H3, brush ||4 of motor M, brush |06 and conductor |05 to the negative terminal of the source of electrical energy |00.

Further upon relay switch arm |96 closing contact |96A, energization of relay |4| will also be effected, since the relay |4| will then be electrically connected to the source of electrical energy |00 from the positive terminal upon arm |30 closing segment |33A, through conductor |04, switch arm |02, Contact |50, conductor |19, switch arm |99, yContact |96A, conductor |91, conductor 2|5, conductor 3, solenoid 4|, conductor |40, ring |32, switch arm |30, switch segment |33A, solenoid A, and conductor 05 to the negative terminal of the source of electrical energy |00. The relay switch arm 203 moreover will upon closing Contact 204 eilect a holding circuit for the latter solenoid |4| by shunting relay switch |99 through conductor H2, conductor |95, switch arm |94, contact 204, and switch arm 203 connected to the conductor |91.

Upon energization of the solenoid |4| the relay switch |43, normally biased under spring tension to an open position, will under the elec tromagnetic force ol' the 'solenoid |4| close contact |42 and thus effect a second holding circuit by shunting switch arm 203 through the electrical conductors 2|9 and |95 for maintaining the solenoid |4|, the circuit to the commutator ring |32, and the circuit to motor M energized should the circuit 2|5 be broken, while the arm |30 is in contacting relation with one of the segmental contacts I 33A through K.

A relay switchL arm 220 controlled by the solenoid |162 is normally biased under spring tension so "as to close contact 22| for normally maintainin'gthe circuit 2|5 closed. However, upon energization of the solenoid |92 by the motor driven arm |30 contacting switch segment |33K as previously described the relay switch arm 220 will be biased under the electromagnetic for-ce of the solenoid |62 so as to open contact 22|. The energizing circuit for the solenoid |92 is connected from the positive terminal of the source of electrical 'energy |00 through conductor |04, switch arm |02, .contact |50, conductor H2, conductor |95, conductor 2|0, switch arm |43, contact |42, solenoid |4l, conductor |49, ring |32, arm |30, switch segment |33K, conductor |36K, conductor |63, solenoid |82, conductor l5! and conductor |05 to the negative terminal of the source of electrical energy |90. However, -due to the holding effect of the relay switch arm |43 the circuits to the solenoid |4|; the circuit through the segmental contact |33K and circuit to the motor M will continue to be energized and the motor M continues to drive the arm |30 along the segmental contact HSK, so long as the same is in contacting relation with the segment |33K.

A switch arm '239 connected to the conductor |163 is normally positioned so as to close a contact 23| to which there is connected an electrical conductor 232. rIhe conductor 232 is connected to the conductor 200 at the point 233,

The solenoid |4| is formed of a relatively low resistance while solenoid |98 has a relative high resistance, thus upon the arm |30 contacting the segmental contact |33K, the potential drop across the relatively high resistance solenoid |98 is reduced, since the segmental contact 33K is connected to the negative side of the solenoid |98 at the point 233 through the conductor 232 and to the negative terminal of the source of electrical energy through the conductors 200, |05 and resistance 20|. Such decrease in the potential drop across the solenoid |98 causes a suicient deenergization of the solenoid |98 so that the relay arm 203 is released under spring tension opening contact 204 and causing spring tensioned arm |94 to'close contact |93.

As previously set forth, the arm |30 contacting the segmental contact |33K causes energization of the solenoid |62, whereupon switch relay arm |60 will. close contact |58 initiating the charging operations of the condenser |54 previously noted and preventing firing of the electronic valve |44 by placing a negative charge on the control grid |48.

Moreover, upon the arm |30 moving ofi of the segmental contact 133K and on to the insulation member '|35 so as' to open the contact 33K, the solenoids i4! and |62 will be deenergized. The deenergization of solenoid |4| will cause relay switch |43 to open contact |42. Thus the circuits controlling the motor M; the solenoid |4'l; the solenoid K; and the solenoid |62 will be opened.

Upon deenergzation of the solenoid |92 the lswitch varm |60 vnll be biased under spring tension so as to open contact |59 and the condenser discharging operation will once again repeat itself.

However, if the switch |16 be moved in a clockwise direction so as to contact the open contact |11 it will be seen that the discharge -circuit for the condenser |54 would remain open and thus the electronic valve |44 may be held from firing by the charge on the condenser 54.

In lorder to initiate operation of the control system a. push button 250 is provided for closing contacts 25| and 252. Contact 25| is connected to conductor |19, while contact 252 is connected to conductor |91 so as to shunt contacts |96 and |96A upon push button 250 closing contacts 25| and 252. Thus the operation of the control system may be manually initiated.

In order to effect selective manual operation of the respective boot control solenoids A through J, there are provided the manually operable switches 260A through 260J, arranged so as to normally close the contacts 26|A through 26|J, which are connected through the switch arms 299A. to 299J in series in the conductor 2 l5.

The switches 290A through 260J are adapted to be manually operated so as to selectively open the respective contacts 2'6IA through 26|J and close contacts connected respectively to the conductors |36A to |36J as shown in Figure 1, so that energization of the solenoids A to J may be manually controlled by the pilot of the aircraft. The energizing circuit for the solenoids A--J is connected from the positive terminal of the source of electrical energy |00 through conductor |94, switch arm |02, contact |50, conductor H2, conductor |95, switch arm |94, contact 204, switch arm 203, conductor |91, switch arm 260, contact 29|, conductor |36, solenoid J-A connected to conductor |36, and returning through conductor |95 to the negative terminal of the source of -electrical energy |00.

In the case of the boot control solenoid K the switch 230 is arranged to be manually operated so as to open contact 23| and close contact 219. Contact 210 is connected through a conductor 212 to the conductor |19 and thereby to the positive terminal of the source of electrical energy l 99 so that upon switch arm 23| closing contact 210 a circuit is completed for energizing solenoid K from the positive terminal of the source of electrical energy |00 through conductor |04, switch arm |02, contact |50, conductor |19, conductor 212, contact 210, switch arm 23|, conductor |36K, solenoid K and through conductor |05 to the negative terminal of the source of electrical energy |00.

In the operation of the automatic control system, a cycle of operation may be initiated by energizing relay solenoid |98 and thereby closing its 'transfer contacts `203 and 204. The relay solenoid |98 may be energized momentarily by either pressing the manual push button 250 or by closing the relay contacts |96 and |96A of the plate relay solenoid |9| through operation of the electronic valve |44 as explained. Once energized the relay solenoid remains energized deriving its power through its own contact arrangement until the contact arm |30 of the motor driven timer reaches position |33K. `Since relay solenoid |4| has a lower resistance than relay solenoid |98 and relay solenoid |4| is shunted across the solenoid |98 when contact arm |30 closes segmental contact 33K the potential drop across relay solenoid 99 decreases permitting relay switch arm 203 to be biased under spring tension so as to open contact 204 and cause relay switch arm |94 to close contact |93.

rihe cycle of operation is terminated upon arm |39 opening contact |33K and resting on the insulation member |35.

The time interval between cycles of operation is of course determined by the interval of discharge of the condenser |54 through the resistance selected by the switch |16, while the interval of inflation of each boot element is controlled by the speed of rotation of the motor M which may be increased or decreased through switch |20.

Only one set of solenoids A, B, C, D, E, F, G, H, and J, may be manually operated at a time. This is due to the fact that all of the switches 200A through 260.] are connected in series with each other and by reversing the position of any one of them causes the power supplied to all of the succeeding switches to be broken.

Moreover operation of the `manually controlled switches 260 will not terminate the operation of the motor M nor the operation of the solenoids A to K controlled thereby since the motor M and solenoids A to K rem-ain energized through the arm |30 due to the contact arrangement of the relays |98 and |4I, until such time as the arm |30 moves to the insulation member |35, whereupon the solenoid |4| is deenergized and switch arm |43 opens contact |42 deenergizing the motor M. Upon switch arm |43 opening contact |42, the motor circuit is deenergized so long as one of the switch arms 260 is in open relation to a Contact 26|. The circuit for the motor M is reenergized upon the switch arms 260A--J once again closing the contacts 26 |A-J.

If the switch be adjusted to open contact |11 for single cycle operation, the cycle of operation will terminate when the switch arm |30 rests solely on the insulation member |35 after opening contact 133K. Another cycle of operation may be then initiated by closing push button 250. In any of the other positions of the switch |16 automatic operation is effected by electronic valve |44 firing at the termination of the delay period required for the charge on the condenser |54 to leak off through the resistances selected by switch |16.

Although one embodiment of the invention has been illustrated and described, various changes in the form and relative arrangement of the parts, which will now appear to those skilled in the art, may be made without departing from the scope of the invention. Reference is, there- I fore, to be had to the appended claims for a dennition of the limits of the invention.

What is claimed is:

1. In an ice elimination system having a plurality of ice eliminating units, motor means operating said ice eliminating units in a predetermined cycle of operation, and electronic valve means for controlling the said motor means so as to successively `provide a predetermined delay period between each of the cycles of operation of i said ice eliminating units, and operator-operative means for adjusting the said predetermined delay period.

2. In an ice elimination system having a plurality of ice eliminating units, motor means operating said ice eliminating units in a predetermined cycle of operation, and means controlled by the operation of said motor means for eiecting cessation of operation of said motor means at the end of said cycle of operation, and electronic valve means controlled by said motor means for re-initiating operation of said motor means after a predetermined delay period.

3. In an ice elimination system having a plurality of ice eliminating units, electric motor means energized for a predetermined period of operation, switch means operated by said motor means for actuating said units in a predetermined cycle of operation, an electronic valve having an anode, a cathode and a control grid,

a capacitor connected between the grid and the cathode, means controlled by said switch means for alternately charging and discharging said capacitor for controlling the operation of said electronic valve, means controlled by said switch means for de-energizing said electric motor means at the end of said cycle of operation, and means connected to the anode of said electronic valve for re-energizing said electric motor means after a predetermined delay period controlled by said capacitor.

4. In an ice elimination system having a plurality of ice eliminating units, electric motor means energized for a predetermined period of operation, switch means operated by said motor means for actuating said units in a predetermined cycle of operation, an electronic valve having an anode, a cathode and a control grid, a capacitor connected between the grid and the cathode, first relay means controlled by said switch means for alternately charging and discharging said capacitor for controlling the operation of said electronic valve, second relay means controlled by said switch means for de-energizing said electric motor means at the end of said cycle of operation, and third relay means connected to the anode of said electronic valve for rre-energizing said electric motor means after a predetermined delay period controlled by said capacitor.

5. In an ice eliminating system having a plurality of ice eliminating units, manually operable means for effecting selective operation of said ice eliminating units, and means for operating said ice eliminating units in a predetermined cycle of operation which cycle of operation is interrupted by the manual operation of the rst mentioned means.

6. In an ice elimination system having a plurality of ice eliminating units, means for operating said ice eliminating units in a predetermined cycle of operation, and manually operable switch means for selective operation of said ice eliminating units during such cycle of operation and. independently thereof.

'1. A time delay circuit controlling apparatus comprising, an electronic valve for controlling said circuit, electric motor means energized for a prodetermined period for controlling the operation of said electronic valve, means controlled by said electric motor means for eilecting deenergization of said electric motor means at the termination of said predetermined period, and means in said circuit and controlled by said electronic valve for effecting re-energization of said electric motor means after a predetermined delay period.

8. A time delay circuit controlling apparatus comprising an electronic valve having an anode and cathode connected in said time delay circuit and a control grid, a capacitor connected between the grid and cathode, electric motor means, relay means operated by said electric motor means for charging the capacitor and after the charging of said capacitor the relay means being operated by said electric motor means in such a manner as to simultaneously d-eenergize said electric motor means and effect the discharge ofv said capacitor, means for retarding the discharge of said capacitor, and means in said time delay circuit for effecting the reenergization of said electric motor means after a predetermined delay period.

9. The combination, comprising an electric motor, an energizing circuit for said motor, a rotatable switch arm driven by said motor, a plurality of switch segments for circuits controlled by said switch arm, said switch segments successively closed and opened by operation of said switch arm, a relay means operated upon closing one of said segments for opening another` circuit, and another relay means for opening thel energizing circuit of said Inotor upon said switch arm opening said one switch segment.

10. The combination, comprising an electric motor, an energizing circuit for said motor, a rotatable switch means driven by said motor, a plurality of switch segments for circuits controlled by said switch means, said switch segn ments successively closed and opened by operation of said switch means, means for opening the energizing circuit oi said motor upon said switch means opening one of said switch segments, and means conditioned by said switch means for closing the energizing Circuit for said motor after a predetermined delay period.

11. The combination comprising an electric motor, an energizing circuit for said motor, a plurality of switch contacts, means actuated by said electric motor for successively closing and opening said switch contacts, an electronic valve having a plate circuit and a control grid circuit, a capacitor connected in said control grid circuit, a first relay means connected in said plate circuit, second relay means for controlling the charging and discharging of said capaci-tor, said second relay means energized upon the closing of one of said switch contacts for effecting the charging of said capacitor, and said second relay means deenergized upon the opening ci said one switch contact for effecting the discharging of said capacitor, said capacitor upon discharging supplying a bia-s -to said control grid for controlling said rst relay means, and said first relay means controlling the energizing circuit for said electric motor.

12. The combination with an airfoil surface; of means for removing ice therefrom, an electric motor, a first circuit for energizing said electric motor, switch means driven by said electric mo tor for cyclically operating said ice removing means for predetermined time intervals, an electronic valve having a plate circuit and a control grid circuit, a capacitor connected in said control grid circuit, a charging circuit for said capacitor, a discharging circuit for said capacitor, a first relay means connected in said plate circuit, a second relay means, a second circuit for energizing said second relay means, said second circuit closed at one position oi said switch means and opened at a succeeding position of said switch means, said second relay means energized upon the closing of said second circuit so as to close said charging circuit for said capacitor, and said second relay means opening said charging circuit upon the deenergization thereof and closing said discharging circuit for eiiecting a discharging operation of said capacitor, a third relay means controlling said motor circuit and controlled by the motor driven switch means, said third relay means simultaneously opening said rst motor circuit upon the opening of said second circuit .by the switch means, said capacitor during the discharging operation supplying a bias to said control grid for restraining energization of the rst relay means in the plate circuit for a predetermined delay period, and said rst relay means eiecting 'the closing of the first motor circuit at the termination of said delay period for re-energizing said electric motor for cyclically operating said ice removing means.

13. In an ice elimination system having a plurality of ice eliminating units, electric motor means energized for a predetermined period of operation, switch means operated by said motor means for successively actuating said units in a predetermined cycle of operation, an electronic valve having an anode, a cathode and a control grid, a capacitor connected between 'the grid and the cathode, nrst relay means controlled by said switch means for alternately charging and discharging said capacitor for controlling the operation of said electronic valve, secon-d relay means controlled by said switch means for deenergizing said electric motor means at the end of said cycle of operation, and third relay means cone nected to the anode of said electronic valve for re-energi-zing said electric motor means after a predetermined delay period controlled by said capacitor, and a plurality of manually operable switches connected in series for effecting selective operation of said ice eliminating units independently of said motor means.

WILLIAM B. POND. FRANK J. HART.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,880,367 Stansbury et al. Oct. li, 1932 1,937,869 Brown Dec. 4, 1933 2,127,080 Barker et al Aug. 16, 1938 2,250,847 Torkelson July 29, 1941 2,358,804 Holloman et al. Sept, 26, 1944 2,373,255 McGoldrick Apr. 10, 1945 

